1. Field of the Invention
The present invention relates in general to analog-to-digital converters. More particularly, the invention is directed to the structure of an analog-to-digital converter utilizing a superconductor.
2. Description of the Prior Art
When a certain material is in the superconducting state, it becomes totally diamagnetic and will not develop a potential difference across it even though a finite amount of steady current flows through it.
This phenomenon of superconductivity has the potential to be used in a very broad range of applications including power generation by magnetohydrodynamics (MHD), power transmission, power storage, magnetic levitational trains, electromagnetically propelled ships, as well as very sensitive measurements of magnetic fields, high frequency, radiation, etc. in such instrumentation fields as nuclear magnetic resonance (NMR), pionic therapy and laboratory equipment used in high-energy physics. Another potential application of superconductivity is in electronic devices of the type including Josephson junction elements which are anticipated to realize circuits that consume less power and operate at faster speeds than conventional devices.
Superconductivity has so far been observed only at cryogenic temperatures. Even Nb.sub.3 Ge which is the superconducting material having the highest superconducting transition temperature Tc does not exhibit superconductivity unless the temperature is below 23.2 K. In order to bring about superconductivity, it has been required to cool the superconductor material to its Tc using liquid helium having a boil point of 4.2 K. However, the use of liquid helium is technically difficult and is very expensive because of the need to employ large cooling facilities including liquefying equipment. This has been a great obstacle in commercializing the potential applications of superconductivity.
Quite recently, it has been reported that sintered composite oxides are superconductors that are capable of exhibiting superconductivity at higher critical temperatures. This discovery has triggered active research efforts to commercialize technology of superconductivity using non-cryogenic superconductors. While various composite oxides have been reported as promising non-cryogenic superconductors, those which are based on Y-Ba-Cu, La-Ba-Cu, or La-Sr-Cu systems and which have crystallographic structures similar to perovskite are particularly interesting since they make the transition to a superconducting state at the temperature of liquid nitrogen and higher.
These new superconducting materials make it possible to exploit the phenomenon of superconductivity under conditions that are closer to those of the natural environment. In order to tap this potential, active research work is underway in many fields of industry and some scientists even predict that the technology of superconductivity is one of the last major breakthroughs to be made in this century which will have dramatic impact on industry.
The present invention has been accomplished as a result of intensive studies made by the present inventors in order to find an effective way of utilizing the recently reported new superconducting materials. It provides a novel analog-to-digital converter as a device that exploits the potential of these superconducting materials.